Assessment of errors and biases in retrievals of X_CO₂, X_CH₄, X_CO, and X_N₂O from a 0.5 cm^–1 resolution solar-viewing spectrometer

• Main Authors: J. K. Hedelius, C. Viatte, D. Wunch, C. M. Roehl, G. C. Toon, J. Chen, T. Jones, S. C. Wofsy, J. E. Franklin, H. Parker, M. K. Dubey, P. O. Wennberg
• Format: Article
• Language: English
• Published: Copernicus Publications 2016-08-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/9/3527/2016/amt-9-3527-2016.pdf

Bruker&trade; EM27/SUN instruments are commercial mobile solar-viewing near-IR spectrometers. They show promise for expanding the global density of atmospheric column measurements of greenhouse gases and are being marketed for such applications. They have been shown to measure the same variations of atmospheric gases within a day as the high-resolution spectrometers of the Total Carbon Column Observing Network (TCCON). However, there is little known about the long-term precision and uncertainty budgets of EM27/SUN measurements. In this study, which includes a comparison of 186 measurement days spanning 11 months, we note that atmospheric variations of X_gas within a single day are well captured by these low-resolution instruments, but over several months, the measurements drift noticeably. We present comparisons between EM27/SUN instruments and the TCCON using GGG as the retrieval algorithm. In addition, we perform several tests to evaluate the robustness of the performance and determine the largest sources of errors from these spectrometers. We include comparisons of X_CO₂, X_CH₄, X_CO, and X_N₂O. Specifically we note EM27/SUN biases for January 2015 of 0.03, 0.75, &ndash;0.12, and 2.43 % for X_CO₂, X_CH₄, X_CO, and X_N₂O respectively, with 1<i>σ</i> running precisions of 0.08 and 0.06 % for X_CO₂ and X_CH₄ from measurements in Pasadena. We also identify significant error caused by nonlinear sensitivity when using an extended spectral range detector used to measure CO and N₂O.